Bleaching of polyacrylonitrile fibers



BLEACHING OF POLYACRYLONITRILE FIBERS Harry W. Coover, Jr., James E. Guillet, and Emmett V. Martin, Kingsport, Tenn., assignors to Eastman Kodak \fompany, Rochester, N. Y., a corporation of New ersey No Drawing. Application January 3, 1952, Serial No. 264,848

3 Claims. (Cl. 8-107) This invention relates to a process for bleaching various types of polyacrylonitrile fibers, and more particularly to a process for bleaching such fibers with acid solutions.

The relatively new and important classes of synthetic fibers as produced from homopolymers of acrylonitrile and copolymers of acrylonitrile with other polymerizable fibers have many potential large scale applications because of their excellent physical properties. Depending upon the composition of the acrylonitrile polymer, the fibers are produced by melt spinning, dry spinning or wet spinning,

In most cases, regardless of what spinning method is employed, or how the composition of the copolymer is prepared, the resultant fibers are not absolutely free of color. Most of these acrylonitrile polymer fibers have a light yellow to tan color. Because of this undesirable color problem the acrylonitrile polymerfibers are restricted from many potential applications where color control is an important requirement.

Attempts to bleach the nitrile fibers by employing such reagents as hydrogen peroxide, hypochlorite and other bleaching agents commonly employed in the art for bleaching fibers and fabrics results in little or no improvement in color. The application of many of these reagents actually increases the color and degrades the fibers.

It is an object of our invention to produce white, lustrous fibers. Another object of this invention is a method of treating acrylonitrile polymer and copolymer fibers to remove undesirable color therefrom. Other objects will appear hereinafter.

We have made the important discovery that the undesirably colored nitrile fibers can readily be bleached to white fibers by washing in acid solutions. We have found that either inorganic and organic acids may be advantageously employed as bleaching agents. The acid concentration that can be used in the bleaching operation ranges from very dilute solutions to concentrated solutions. The most efiective concentration of acid is determined by the type of acid being employed, temperature at which it is to be employed and the composition of the fiber to be bleached. The more concentrated the acid solution the more rapid the bleaching and the higher the temperature, the more rapid the bleaching. High concentrations of inorganic acids have to be employed with extreme care, since there is danger of hydrolyzing the polyacrylonitrile fibers.

Under the proper conditions of temperature and concentration of acid, there is no hydrolysis of the polyacrylonitrile fibers. In general, the preferred acid concentration is 1 to 10% and the preferred temperature range is 20 C, to 100 C. A treating time of from one hour to three hours may be advantageously employed.

As inorganic acids we can advantageously employ the oxygen acids of phosphorus (i. e. metaphosphoric, orthophosphoric, hypophosphoric, pyrophosphoric, metaphos phorous, orthophosphorous, hypophosphorous orpyrophosphorous acid). As anhydrides we can advantageous- -1 a r s a T. h itai'ltiiiiti 'iiUillVE FiPssos OR 2.751.277

United States atent O Hce Patented June 19, 1956 1y use those of the oxygen acids of phosphorus, i. e. oxides 2 751 of phosphorus, such as phosphorus trioxide (P203), phosphorus tetraoxide (P204) and phosphorus pentoxide (P205). Also sulfuric acid and sulfurous acids may be employed.

As organic acids we can advantageously employ oxalic acid, acetic acid, trifluoroacetic acid, alkane sulfonic acids, aromatic sulfonic acids, alkyl phosphoric and phosphorous acids, alkane phosphonic acids and alkene sulfonic acids. Typical alkane sulfonic acids include methanesulfonic, ethanesulfonic, propane 1 sulfonic, propane 2 sulfonic, n-butane-1-sulfonic, isobutanel-sulfonic, sulfoacetic, fi-hydroxy sulfonic, etc. acids (e. g. alkane sulfonic acids containing from 1 to 4 carbon atoms). Typical aromatic sulfonic acids include benzenesulfonic, p toluenesulfonic, o toluenesulfonic, mbenzenedisulfonic, 1,3,5 benzenetrisulfonic etc. acids (e. g, a sulfonic acid of the benzene series). Other useful aromatic sulfonie acids include naphthalene-a-sulfonic, naphthalene fl sulfonic, 1,5 naphthalene disulfonic, 2, 6 naphthalenedisulfonic, etc., acids (e. g. a sulfonic acid of the naphthalene series). phosphoric acids include monomethyl acid orthophosphate, monoethyl acid orthophosphate, mono n propyl acid orthophosphate, monoisopropyl acid orthophosphate, mono n butyl acid orthophosphate, monoisoamyl acid orthophosphate, mono n octyl acid orthophosphate, mono n capryl acid orthophosphate, dimethyl acid orthophosphate, diethyl acid orthophosphate, ethyl isoamyl acid orthophosphate, ethyl n-octyl acid orthophosphate, ethyl-n-capryl acid orthophosphate, di-n-butyl acid orthophosphate, n-butyl n-amyl acid orthophosphate, dimethyl acid pyrophosphate, diethyl acid pyrophosphate, di-n-propyl acid pyrophosphate, diisopropyl acid pyro' phosphate, di-n-butyl acid pyrophosphate, diisoamyl acid pyrophosphate, di-n-octyl acid pyrophosphate, di-ncapryl acid pyrophosphate, etc. (See Alder and Woodstock Chem. In., vol. II (1942), p. 516.) Typical alkyl phosphorous acids include: monomethyl acid phosphite, monoethyl acid phosphite, mono-n-propyl acid phosphite, monoisopropyl acid phosphite, monoisobutyl acid phosphite, monoisoamyl acid phosphite, dimethyl acid phosphite, diethyl acid phosphite, di-npropyl acid phosphite, diisopropyl acid phosphite, din-butyl acid phosphite, diisobutyl acid phosphite, monoethyl acid hypophosphite, monoisobutyl acid hypophosphite, etc. Alkyl phosphoric and phosphorus acids (i. e. alkyl acid esters of acids of phosphorus) containing from 1 to 10 carbon atoms in the alkyl group have been found to be especially useful. Alkyl acid esters of acids of phosphorous containing from 1 to 5 atoms in the alkyl group constitute a preferred class. Typical alkane phosphonic acids include methane phosphonic, ethane phosphonic, n-propane phosphonic, isobutane phosphonic (isobutyl phosphonic), isoamyl phosphonic (isoamyl phosphonic), etc, acids (e. g. alkane phosphonic acids containing from 1 to 5 carbon atoms). Typical alkene phosphonic acids include: vinyl phosphonic, propene 2 phosphonic, u-phenylvinyl phosphonic, etc. acids (e. g. an a,fi-unsaturated, alkene phosphonic acid containing from 2 to 8 carbon atoms in the alkene group). Alkene phosphonic acids useful in practicing our invention are described in U. S. Patent 2,365,- 466, dated December 19, 1944.

The preferred diluent for the acid solutions is water. However, other diluents such as alcohols, ketones and the like can be employed. After the acid bleaching treatment, the acid is washed out of the fibers with water.

The following examples will further illustrate the invention.

Typical alkyl Example 1 A 10 g. skein of a polyacrylonitrile fiber which was light yellow in color and had a tenacity of 4 g./denier, extensibility of 20 per cent, was soaked in a per cent oxalic acid solution at 50 C. for 3 hours. The skein was then washed free of acid and dried. The resultant polyacrylonitrile fiber was completely free of color and exhibited no loss in physical properties.

Example 2 A g. skein of a polyacrylonitrile fiber which was light tan in color and had a tenacity of 3.8 g./denier, extensibility of 17 per cent, was soaked in a 1 per cent phosphoric acid solution at 60 C. for 1 hour. The resultant fiber was completely free of color and retained its original physical properties.

Example 3 A ribbon prepared from a 60-40 copolymer of acrylonitrile-vinyl chloride which was tan in color and had a tenacity of 2.8 g./ denier and a 25 per cent extensibility was soaked in 10 per cent phosphorous acid at 30 C. for 2 hours. The resultant ribbon was washed free of acid and dried. The ribbon was completely free of color and exhibited no loss in physical properties.

Example 4 A 10 g, skein of a fiber prepared from a copolymer of acrylonitrile-acrylamide, 90-10, was light yellow in color and had a tenacity of 3.8 g./denier and a 25 per cent extensibility. The skein was soaked in a 1 per cent sulfuric acid solution at 45 C. for 1 hour. The skein was washed free of acid and allowed to dry. The resultant fiber was completely free of color and exhibited no loss in physical properties.

Example v5 A 10 g. skein of a polyacrylonitrile fiber which was light yellow in color and had a tenacity of 4.5 gJdenier and a 19 per cent extensibility, was soaked in a 5 per polymers having been made in the absence of oxalic acid which consists of bleaching the fibers only in a solution of oxalic acid and then washing the fibers to remove the acid therefrom.

2. The process of claim 1 in which the acid treatment of the fibers is conducted at a temperature within the range of 20 C. to 100 C. for 1 to 3 hours, with an acid concentration of 1 to 10%.

3. The process of bleaching polyacrylonitrile fibers said polyacrylonitrile having been made in the absence of oxalic acid which consists of soaking the fibers only in a 5% oxalic acid solution for 3 hours at C., and then washing the acid from the fibers.

References Cited in the file of this patent UNITED STATES PATENTS 2,160,931 Wiley June 6, 1939 2,432,447 Scheiderbauer Dec. 9, 1947 2,503,244 Coover Apr. 11, 1950 2,503,245 Coover Apr. 11, 1950 2,579,451 Polson Dec. 18, 1951 2,629,711 Stanin Feb. 24, 1953 2,643,934 Scheiderbauer June 30, 1953 FOREIGN PATENTS 913,939 France Sept. 24, 1946 

1. A PROCESS OF REMOVING COLOR FROM FIBERS MADE OF HOMOPOLYMERS AND COPOLYMERS OF ACRYLONITRILE SAID POLYMERS HAVING BEEN MADE IN THE ABSENCE OF OXALIC ACID WHICH CONSISTS OF BLEACHING THE FIBERS ONLY IN A SOLUTION OF OXALIC ACID AND THEN WASHING THE FIBERS TO REMOVE THE ACID THEREFROM. 